Thế năng tại vị trí sâu 2m là
Wt = mgh = 3.g.(-2) = -6g (J)
Nếu : gia tốc trọng trường:
g = 10m/s^2 thì Wt = -60 (J)
g = 9,8m/s^2 thì Wt = -58,8 (J)
Đáp án:
Wt=-60J
Giải thích các bước giải:
Thế năng tại điểm đó là:
\[{{\text{W}}_t} = mgh = 3.10.\left( { - 2} \right) = - 60J\]
Cho 16,8g hỗn hợp X gồm Cu,Mg,Fe tác dụng với clo dư ở nhiệt độ cao đến khi các phản ứng xảy ra hoàn toàn thu được 48,75g hh rắn. Mặt khác, 0.8 mol hh X tác dụng vừa đủ với 600ml đ HCl 2M. Tính số mol mỗi kim loại có trong 16,8g hh X.
READING PASSAGE 1 MEET THE ANCESTORS What makes you who you are? Part of the answer is in your family's past. Become a detective and find clues to your family history. 1. When you look in the mirror, do you see your father's smile? Maybe you take after your mother or look like a grandparent? That's because of DNA. Our DNA contains genes that make each person in the world different - no two people look, think or act the same. We pass down our genes through generations. Scientists can test your DNA to find out which part of the world your ancestors were from. 2. Your family's history may be a mystery to you, but there's a way to find out about it. It's called genealogy, and it's the study of the people you are related to. Genealogy helps you put together your family history. It starts with the relatives you know, such as parents and grandparents, and then you can learn about ancestors who lived and died before you were born. 3. It isn't difficult to learn about your past. You can begin by asking your relatives questions about your ancestors. While you are talking with family members, take notes. This helps you organise any information you get. Make sure you write down any names, dates or places people mention. Then you can draw a family tree with your name at the top. Then you would add all the relatives from you to your great grandparents so you can see how everyone is related. 4. If there any blank boxes in your tree it's time for some detective work! Many people begin at a library where they can look for family names in old newspapers. Public records are usually a very good thing to look at too. They have information about births, marriages and death certificates too. Some records show when people moved to a country. Sometimes, records tell you where people went to school and what their job was. You can also search the Internet. With every bit of research that you do, you are discovering your family's history. Task 1: Look at the sentences below about studying your family history. Read the text to decide if each sentence is correct or incorrect. Write T (True) or F (False). 1. We look the way we do because of the genes in our DNA. 2. A DNA test can show where in the world our ancestors lived. 3. You can find out the number of relatives you have in a DNA test. 4. Genealogy is the history of our past and present family members. 5. Relatives who are alive could have information about ancestors. 6. A family tree shows how you are relatedto other people in your family. 7. A detective can help you to find information about your family. 8. It is possible to buy old newspapers at some libraries. 9. Public records tell you when people were born. 10. The text says that websites can help you find information about your ancestors. Task 2: Find the underlined words in the text and think about what they mean. Then circle the correct meanings below. 1. take after: to follow somebody / to be like somebody 2. look like: to have a similar appearance / to seethings you enjoy 3. pass down: transfer to / respect the next generation 4. relative: family member / close friend 5. find out: to take outside / to discover or learn 6. look for: to be similar to / to try to find
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